Heretofore, a printed circuit rf switchable step attenuator for use in the Gigahertz range has been constructed by using a pair of single pole, double throw switches arranged to allow selective switching of the signal path between a straight-through conductor and an attenuator network such as a T-pad or a pi-pad. High performance has been difficult to attain with this type of circuit arrangement, particularly where broadband response is required, for essentially two reasons. First, proper ground connections for the shunt resistor or resistors in the attenuation network have been difficult to achieve because the usual grounding means (plated over-edges and plated through-holes) have a large amount of parasitic series inductance associated with them at microwave frequencies. Thus, placement of the shunt resistor with respect to the ground terminal is very critical. Second, in order to couple the necessary D.C. bias potential into the rf circuit for switching purposes the use of high impedance "flying lead" inductors is necessary. Both these past requirements have made construction of broadband attenuators very expensive and difficult to manufacture with a high degree of repeatability.
Additionally, the use of a pair of single pole, double throw switches requires the use of at least two diodes in series with the signal path of all times. Since series diodes are the main cause of insertion loss in a circuit of this type, the use of multiple series diodes substantially increases the insertion loss and this is extremely undesirable when operating the circuit in its low attenuation state.